brother-in-law (elder); stepbrother (elder)
Refers to one's elder brother-in-law (spouse's elder brother) or elder stepbrother. The term 兄 (あに) specifies an elder brother; for a younger brother-in-law, 義理の弟 (ぎりのおとうと) is used.
My brother-in-law is getting married next month.
I live with my elder stepbrother.
Compound of 義理 (ぎり, 'in-law; duty') + の (possessive particle) + 兄 (あに, 'elder brother'). The term follows the pattern of specifying a relative by marriage or step-relationship.